Stress analysis model of GaN based on angle-resolved Raman spectroscopy accounting for birefringence effect

Gallium nitride (GaN) has wide application prospects in various fields such as light-emitting diode chips, radio frequency chips, high-energy lasers, and energy conversion devices. Complex preparation processes and extreme working environments generate complicated stress/strain states and distributions inside and on the surfaces of the GaN devices, thus affecting their performances and reliabilities. It is a common requirement for the design, manufacturing, and application of GaN devices to develop an experimental method analyzing full-field stress, especially decoupling all components of the unknown stress state. This work established an improved theoretical model of angle-resolved Raman for the stress analysis of GaN, which quantified the birefringence effects and provided the generalized analytic relationship between the three in-plane stress components and the Raman shift of GaN under arbitrary geometric and polarization. This work presented the specific expression forms of the equations in typical situations, and the parameters of the model were calibrated through angle-resolved Raman experiments. Verification experiments employing four-point bending demonstrated close agreements between the measured stress components and the prescribed loadings. Finally, the applicability and precision of the proposed model, for component decoupling analysis of the complex stress states, were systematically evaluated based on the experimental results of the stress fields around a circular through-hole of a compressed GaN sample.